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Notable trends during the week of June 24th include:
Cabbage Looper moth counts continue to be extremely high, we are likely seeing the 2nd generation, which is considered the most damaging for brassica crops.
Armyworms have wide host ranges but can be especially damaging in grasses, pastures, and field crops.
One species, in particular, seems to be booming this year. It is called the “Thoughtful Apamea“, which is closely related to glassy cutworm, but habits and host range are largely unknown.
Conversely, True Armyworm is well-studied and we have been collaborating on a project to monitor them in Tillamook County. So far, counts are low, but if you’re interested, trap counts will always be posted here: https://beav.es/ZQM
Beneficial Insects include pollinators, predators, and parasitoids that provide some type of ecosystem service. As natural enemies of pests, their activity tends to lag slightly. We have noted an increase in Syrphidae and Tachinidae flies this week, as monitored by passive sampling techniques.
This “CAUTION” post is similar to one I made a few weeks ago for cole crops; a quick way to highlight a potential problem, in hopes that consultants, gardeners, etc., will do some scouting to investigate if/to what extent they may be affected.
We saw, for the first time this season, some westernstriped cucumber beetle (Acalymma trivittatum) activity on both both weedy volunteer and cropped cucurbits.
This pest is of particular concern because it vectors bacterial wilt, a plant pathogen caused by Erwinia tracheiphila bacteria. Researchers now suspect that, rather than overwintering in the intestinal tract of adult beetles, the bacterium overwinters in the sap of alternate host plants (i.e. volunteer and weedy cucurbit species). The alternate host plants may not show symptoms of being infected, which can make management difficult.
As adult cucumber beetles feed, the beetles become infected with bacterial wilt, and then transmit it to crops. This infection can be direct (feeding on one host then another), or secondary (fecal contamination of already wounded tissue). Once the disease is established, it cannot be managed with pesticides, so ‘awareness’ of cucumber beetle activity levels, and subsequent control if necessary, is considered the best preventative tactic.
A few tips for scouting bacterial wilt in cucurbits:
Melons, squash, and cucumber are considered more susceptible than zucchini and watermelon, but all related plants (Cucurbitaceae) are at riska
Damage can occur quickly – scout 2-3X/week for beetle pressure and wilt symptoms
Symptoms can be immediate on some plants, and not occur until after fruiting on others
Leaves may look dull green, yellowing at leaf margins
Vines wilt during the day, but seem to recover at night
Quick diagnostic test (photos below): stems/vines are cut close to the crown, and a ‘stringy’ sticky substance appears when the two halves are pressed then pulled apart from each other. b
PHOTO CREDITS: Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org
There is a great new eXtension article about biology and management of cucumber beetles in organic farming systems available at: https://beav.es/ZYJ (it’s ok – we’ll use a Beavs shortlink to promote WSU just this once…there’s some great people/research going on up there!)
aDISCLAIMER: regional differences in pathogen expression are likely, do not rely on literature from other areas bDISCLAIMER: may not work for all species or all cases